Means for delaying electrical signals



y 1954 H. N. BEVERIDGE ET AL ,067

MEANS FOR DELAYING ELECTRICAL SIGNALS 6 H1450 WIT/l If;

Filed March,l2, 1948 u 0 C 5 :w LT L 3 F M 9 I C P 7 j Z m i r 4 F. M

V 56 fimmwm m nu NMm dw Z M WM y 1954 H. N. BEVERIDGE ET AL 2,685,067

MEANS FOR DELAYING ELECTRICAL SIGNALS Filed March 12, 1948 4 SheetsSheet2 y 1954 H. N. BEVERIDGE ETAL 2,685,

MEANS FOR DELAYING ELECTRICAL SIGNALS Filed March 12, 1948 4Sheets-Sheet 3 F/Gi/l f 4 2i 44 48 2e 22 23 2a a Patented July 27, 1954UNITED i 'i'ENT OEFICIE MEANS FOR DELAYING ELECTRICAL SIGNALS porationof Delaware Application March 12, 1%8, Serial No. MAM

17 Claims.

This invention relates to means for delaying electrical signals, andmore particularly to an ultrasonic mercury delay line of the tank type.

An object of this invention is to devise an ultrasonic delay line whichis of small size, is rather simple in construction, and yet in whichdelays of a relatively long time may be obtained.

Another object is to provide a multiple-path mercury delay line in whichall of the paths traverse a single pool or body of mercury.

A further object is to devise a construction in which a plurality ofultrasonic mercury delay lines utilize the same pool of mercury, therebyproviding uniform velocities of travel of the compressional waves ineach of such lines.

A still further object is to devise means for independently adjustingthe time delays of each of a plurality of delay lines, in order tocompensate for manufacturing tolerances and circuit dissimilarities, tothereby enable such delays to be brought into equality with each other.

An additional object is to devise an ultrasonic mercury delay linewherein spurious or undesired paths of travel of the energy, which couldresult from spreading of the ultrasonic beam, are substantiallyeliminated.

Still another object is to provide substantially perfect reflectingsurfaces in the metallic tank of a mercury delay line, which surfacesmay be very readily and inexpensively produced.

Yet another object is to devise a multiplereflection ultrasonic mercurydelay line construction which utilizes the mercury very efficiently,thereby reducing the overall dimensions and total weight of such linewithout at the same time reducing the delay time of such line.

A further object is to devise an ultrasonic delay line construction inwhich the side edges of the slightly diverging ultrasonic beam are ineffect clipped off and diverted away from the main beam so as not tointerfere therewith.

The foregoing and other objects of the invention will be best understoodfrom the following description of some exemplifications thereof,reference being had to the accompanying drawings,

Fig. 2 is a horizontal section through a tank or delay line according tothis invention, showing the path of travel or" compressional Wavestherein;

Fig. 3 is a vertical section through the device of Fig. 2, taken alongthe line 33 thereof but on a larger scale;

Fig. 4 is a horizontal section through a modiz'ied constructionaccording to this invention;

Fig. 5 is a schematic diagram corresponding to Fig. 4.- showing thecompressional wave path therein;

Fig. 6 is a partial vertical sectional view similar to Fig. 3 of amodified construction;

Fig. 7 is a section taken along line l"l of Fig. 6;

Fig. 8 is an elevation of another type of delay line according to thisinvention;

Fig. 9 is an end view of the device of Fig. 8;

Fig. 10 is an opposite end view of the device of Fig. 8;

Fig. 11 is a section taken along line H-ll of Fig. 9;

Fig. 12 is a section taken along line l2l2 of Fig. 10;

Fig. 13 is a block diagram of a portion of a radar system utilizing adelay line according to this invention; and

Fig. 14 is a block diagram of a portion of a computer system utilizingthe delay line of Figs. 8-12.

In general, this invention relates to a mercury delay line, whichfunctions to delay broad band intelligence or electrical signals from afew microseconds up to several milliseconds. Such a mercury delay lineconsists of a body of mercury having a pair of spaced electromechanicaltransducers acoustically coupled thereto, one being a transmittingtransducer and the other a receiving transducer. Since the mercury lineexhibits not a long pass but a band pass characteristic, it is necessaryfirst to modulate the incoming electrical intelligence on a carrierwave. This modu lated electrical energy causes the quartz transmittingtransducer to vibrate in a piston-like manner, sending an ultrasoniccompressional wave (one having a frequency on the order of 5-30megacycles, for example) down the mercury column. Upon striking thequartz receiving transducer, the acoustic or compressional wave energyis converted back into an electrical carrier wave signal like theoriginal, which electrical signal is amplified and demodulated to giveback the original intelligence delayed in time. In some cases, it isentirely feasible to operate the mercury delay line without utilizing acarrier wave, the line operating also in this case to delay theelectrical signals impressed thereon.

In general, delays of anywhere from 25 to 10,000 microseconds might bewanted. The velocity of compressional waves in mercury is approximatelyM51300 centimeters per second, so that five feet of mercury correspondsapproximately to a delay of 1,000 microseconds or one millisecond.Therefcot to approximately 50 feet.

Now referring to Fig. 1, in order to provide for longer time delays withdelay tanks of reasonable dimensions, or in order to decrease theoverall length of the delay devices, a box or tank I containing mercuryis used, this box being more or less rectangular in outline and havingopposite reflecting upstanding side walls 2 and 3. A quartz transmittingor input transducer is shown schematically at t and is mounted near oneend of side wall 2, with the vibrating or inner portion thereof lying ina plane which makes a small angle with the inner face of wall 2. Such anangle may be conveniently provided by beveling a portion of the outerface of wall 2. Fig. 1 is a horizontal section through a mercury tankwhich might be used. A quartz receiving or output transducer is shownschematically at 5 and is mounted near the opposite end of side wall 3,with its vibrating portion lying in a plane which is substantiallyparallel to that of the aforesaid portion of transducer 4. The active orinner faces of transducers t and 5 are both acoustically coupled to themercury in tank I.

Fig. 1 indicates several possible patterns of travel of thecompressional wave energy between input transducer 4 and outputtransducer The desired path of travel is indicated by solid lines A andemploys three traverses of the tank i. The beam starts out substantiallyperpendicular to the transmitting face of transducer 6 and is reflectedback and forth between the side walls 2 and 3, with the respectiveangles of incidence being equal to the corresponding angles ofreflection, the beam of compressional Wave energy after three traversesoi the tank impinging on the receiving tranducer 5. A possible spuriousor undesired path between transducers i and 5 is that indicated by thedotted line B, which is the direct path between said transducers andemploys only one traverse of the tank. This path B is possible becauseof undesired and unavoidable spreading of the beam of compressional waveenergy. Still another possible spurious or undesired path of travel ofthe compressional wave energy is indicated by the dot-dash lines 0,which path, similarly to path A, is reflected back and forth between theside walls 2 and 3 with the re spective angles of incidence being equalto the c0rresponding angles of reflection, this path employing fivetraverses of the tank. Path 0 is a result of spreading or divergence ofthe beam. There are other spurious paths as well, employing seven, nine,eleven and so on traverses. The paths A, B and C illustrated are allsubstantially horizontal.

It may be seen that there is only a rather small angle between theoriginal directions of paths A and C, the original directions herereferring to their directions as they emanate from input transducer 3.In the example illustrated in Fig. 1, the tank has been designed for atime delay, or time of travel of the compressional wave therein,corresponding to three traverses of the tank. It should be apparent thatspurious patterns such as C, which involves five traverses of the tank,give an improper time delay and are therefore undesired; such spuriouspatterns are quite serious since they diverge from the desired pathdirection by only very small angles. Moreover, as one goes to designsinvolving a greater number of traverses of the tank, these spuriouspaths become more serious since they diverge or differ from the originaldesired path direction by still smaller angles.

It has been found, according to this invention, that over relativelygreat distances betwen two compressional wave transducers, most of thetransmitted energy is contained within a circle equal in diameter to thetransmitting transducer. However, at distances on the order of inchesand with customarily used circular transducers at ultrasonicfrequencies, even though the diameter of the transducer is quite largeas compared to the wavelength of the energy, the radiation pattern of aplane wave front of uniform energy emanating from such transmittingtransducers has very noticeable minor lobes at the sides of the mainbeam, these lobes having high enough relative amplitudes to be noticed.If this pattern were allowed to develop a design employing say eleventraverses or the tank, a number of spurious paths would be produced clueto the divergence or spreading of the beam (or to the presence of minorlobes), such spurious paths involving nine and thirteen traverses, sevenand fifteen, five and seventeen, etc, due to the symmetry of the minorlobes about the main beam. Thus, it may be seen that, in the design ofFig. 1, one problem which exists is the beam spreading or divergence andthe consequent development of spurious or undesired paths. As willhereinafter appear, this problem has been satisfactorily solvedaccording to the present invention.

Another probl m which has been solved according to this invention is thedevelopment of satisfactory reflecting surfaces for the tank. Theproportion of compressional wave energy reflected at the interfacebetween two dinerent acoustic media depends on the relative acousticimpedances of the two media, being small when the difference between thetwo inipedances is rather small and large when the difference betweenthe two acoustic impedances is rather large.

It has been found that quartz crystals function very effectively astransducers for devices of the type under discussion. For thelongitudinal mode, quartz has an acoustic impedance of 152x10 in C. G.S. units. For the same mode, mercury has an acoustic impedance ofapproximately x10 which is rather close to that of quartz, so thatmercury can be acoustically coupled to quartz in a quite effectivemanner with a minimum of reflection at the quartz-mercury interface;since mercury is a liquid, it may be very advantageously used as thetransmitting medium in an untrasonic delay line. As the term acousticimpedance is commonly used in the art, this quantity is the product ofthe compressional wave velocity in a substance and the density of thatsubstance.

Since substantially perfect reflection of compressional wave energy isdesired at the walls 2 and 3 of the tank, in order to minimize theoverall attenuation of the tank from input transducer 4 to outputtransducer 5, it is very important that a substantial impedance mismatchoccur at the tank side wallunercury interface. In other words, it isnecessary that the side walls 2 and 3 be highly reflecting, to allow aplurality of traverses of the tank to be made without appreciableattenuation of the compressional wave energy. Another characteristicwhich the side walls of the tank, as well as the rest of the tank, musthave is that they be able to contain the mercury and must not chemicallyreact or combine therewith. Steel and stainless steel have been found tobe suitable materials for the walls of a tank containing mercury, fromthe points of view of necessary strength and chemical inertness withrespect to mercury. Steel has an acoustic impedance of approximately 3910 While stainless steel has an acoustic impedance of approximately 430xConsidering the relative acoustic impedances of mercury and steel,however, it appears from calculations that about $4 of the compressionalwave energy striking a mercury-steel interface would pass into the steeland only 6 of the incident energy would be reflected. Experimentsutilizing steel with its surface ground very smooth or very fine bearout these calculations; s eel with a Very fine ground surface forms areasonably good acoustic impedance match to mercury, the reflectedenergy being down 10 db on the incident energy. Therefore, if the walls2 3 of the tank I in Fig. 1 are to be utilized as reflecting surfaces asin said figure, steel with a fine ground surface cannot be, used forsuch walls, since such material forms a reasonably good acousticimpedance match to mercury and not a substantial impedance mismatch asis necessary for good reflection of o0mpressional Wave energy,

It has been found, according to this invention, that, if the steel faceis lightly sandblasted or etched, 100 per cent. reflection ofcompressional wave energy results at the mercury-steel face. Thus, asone passes from a fine ground surface to a rough surface, thetransmission of energy changes from the transmission predicted intheory, and found in practice, to no transmission or total reflection.

Although We do not wish to be limited to any particular theory as to whyan etched or sand-- blasted steel surface provides 10s per cent,redection, as contrasted to only approximately 19 per cent. reflectionwith a finely ground steel surface, the following is our presentunderstanding of the theory behind this phenomenon. Mercury does not wetsteel. Hence, at a sandblasted or etched steel surface, the mercurytouches the steel only at the high spots of such roughened surface,leaving a cushion of air between the mercury and the steel at all thelow points of such surface. Air has an acoustic i "silence of 41.3,which is vastly different from .t of mercury, so that, at themercury-air interface provided. by the roughened surface, there is asubstantial acoustic impedance mismatch, which provides the totallyreflecting characteristic desired. It should be clearly understood thatinvention operates as described above without gard to the truth offalsity of theory ing or tending to explain the operation of the same.

From the above, it may be seen that posible to have a mercury-steelinterface which can be made totally reflecting (when rough.) orabsorbing to the extent of 10 db (when smooth). Moreover, this change inreflection characteristics can be accomplished in a rather simple andinexpensive manner. Thus, the problem of pro viding satisfactoryreflecting surfaces for tank has been solved according to thisinvention.

Figs. 2 and 3 show a construction of ultrasonic delay line accor ing tothe principles just discussed. The tank 6 is substantially rectangularin outline or configuration, is filled with mercury, as indicated, andhas the and output quartz electromechanical transducers and 5.,respectively, located in the pair of upstanding side walls 7 and 8- inthe same Way as such transducers are located in Fig. 1. The active. orinner faces of transducers 4 and 5 are both acous tically coupled to themercury in tank Each of the walls '5 and 8, in addition to beingprovided with apertures for the corresponding transducers i and 5, isprovided with five equally-spaced circular sandblasted areas 9, thecenters of which on both wallsall lie in a common horizontal plane, sothat the circles on each wall are in horizontal alignment with the othercircles on that same wall. The diameter of each of the sandblastedcircles 9 is substantially equal to the diameter of transmittingtranducer 4 and the receiving transducer 5. The interior surfaces ofwalls '1' and 8 are fine ground throughout their areas, except for thesandblasted circular reflectors or areas 9, so that smooth ground steelsurfaces are provided in between such reflectors.

The circular reflectors 9 on wall 3 are staggered or displaced withrespect to those on wall I, in a direction from top to bottom of 2,which figure is a horizontal section through the tank, by an amountwhich depends on the angle between the active or inner face oftransducer 4 and the inner face of wall l, and also on the distancebetween walls 7 and 8. This amount of displacement is made such that thecenter line D of the cylindrical beam of compressional wave energyemanating from transducer s will strike the center of the uppermost (in2) reflector 5 of wall 8, and so that the center line of such beamreflected from said uppermost reflector on wall 8 will strike theuppermost reflector 9 of wall 7.

The tank 6 has five sandblasted reflectors on each of the walls I and 3and, as indicated by the lines D in Fig. 2, which indicate the centerline of the cylindrical beam of compressional wave energy in the travelof such energy through the tank, is designed for eleven traversesthrough said tank. The circular reflectors are provided on the walls inareas where reflection is wanted. The energy from transducer s fallsalmost totall on the upper most reflector of wall 8, since the distanceacross the tank is rather sort and since the diameter of the reflectoris equal to the diameter of the transducer i. Some very small amounts ofenergy, which has spread beyond the original diameter of the beam, falloutside of said uppermost reflector 9, impinge on the smooth steelsurrounding this reflector, and are substantially all absorbed, sincesuch smooth steel is highly absorbing.

The energy reflected from this uppermost re fiector 9 is projectedtoward the second reflector, which is the uppermost reflector ii on walll, since the angle of incidence on the first reflector is equal to theangle of reile tion therefrom. The energy from the first reflector fallsprimarily on the second reflector, which is also of the same diameter astransducer with the spread fall ng outside of the second reflector andagain being substantially all absorbed by the smooth steel surroundingthis reflector.

The same thing happens to the energy reflected from the second reflectortoward and to the third reflector, which is the second reflector fromthe top on wall 2%, and also for each and every refiection throughoutthe eleven traverses oi the tank by the compressional wave beam, sinceall of the reflectors 9 have diameters equal to the diameter of thetransmitting and receiving transclucers and since all of the reflectorsare surrounded by substantially non-refiecting or absorbing smooth steelsurfaces.

Thus, it should be apparent that, throughout its path of travel in thetank, the compressional Wave beam is continuously and successivelyclipped or limited in diameter to one equal to that of the transmittingtransducer. Since most of the transmitted energy is contained within acircle equal in diameter to the transmitting transducer, at least out torelatively great intertransducer spacings, no appreciable amount ofenergy is lost by this beam clipping technique. On the other hand, bythis continuous and successive beam clipping technique, the divergent orside energy of the beam, corresponding to the minor lobes thereof, isprogressively eliminated at each reflector, thus preventing such energyfrom adding up cumulatively. The energy therefore arrives at the outputor receiving transducer 5, never having had a chance to spread out anddevelop a radiation pattern in which there are any appreciable minorlobes. By this technique, the energy path is uniquely defined, spuriouspaths which could be produced by divergence or spreading of the beambeing effectively prevented or eliminated, so that the proper anddesired time delay is positively obtained. Thus, it will be seen that wehave effectively solved the problem of spurious or undesired paths ofcompressional wave energy by eliminating the same.

It should be seen that the tank of Figs. 2 and 3 is of rather simpledesign and may be readily constructed. Each of the steel side walls Iand 8, which may be of stainless steel if desired, is first fine ground,after which a mask with holes therein where reflectors 9 are wanted isplaced over the Wall and sandblasting is applied. If the tank ii isentirely filled with mercury and sealed, an air-filled expansion tank(not shown) of conventional design is provided, this tank having aflexible diaphragm contacting the mercury; such a tank allows forexpansion and contraction of the mercury resulting from changes intemperature.

In the tank design shown in Figs. 2 and 3, much of the mercury is useddoubly by the cylindrical beam, as should be seen from a considerationof the location of the center line D of the beam and of the diameter ofreflectors 9, which have a diameter equal to that of the cylindricalbeam. Thus, the mercury pool or body is used rather efficiently,minimizing the amount of mercury required for the tank,

Figs. 4 and 5 show a modified design according to this invention, inwhich the mercury is used still more efficiently. Fig. 4 is a horizontalsection through the tank, with the input and output electromechanicaltransducers omitted, while Fig. 5 is a diagrammatic illustration of thepath of the compressional wave energy in the tank of Fig. 4. The tank H3is substantially square in outline and has four steel side walls H, 12,I3 and it. Each of these walls has a planar inner face, with theexception that, at one end, wall I I has a small portion I la whichangles inwardly at an angle of approximately 45 with respect to theplane of the remainder of wall iI. Therefore, walls Ii and I2 intersectat an angle of approximately 45". instead of 90, as do the other pairsof intersecting walls. Wall i i has an aperture I5 therein adjacent oneend thereof, in which an input transducer (not shown) may be mounted. Asin the modification of Figs. 2 and 3, the transducer is adapted to bemounted with its active face lying at a small acute angle to the innerface of wall I I, this angle being conven- 8 iently provided bybevelling a portion of the outer face of said wall.

Wall I2 has a similar aperture i6 therein in which may be mounted anoutput transducer (not shown). Aperture it has a diameter equal to thediameter of aperture I5, and the output transducer is adapted to bemounted therein with its responsive face at a similar small angle to theinner face of Wall i2.

The inner face of walls 53 and It are each provided with four spacedaligned sandblasted circular reflectors i'i, each of these reflectorhaving a diameter equal to the diameter of transducer apertures i5 andit, all of the inner surfaces of these walls except for the reflectorsbeing smooth ground or line ground, The inner faces of Walls Ii and i2are each provided with three spaced aligned sandblasted circularreflectors It, each of which has a diameter equal to the diameter oftransducer apertures I5 and I6, all of the inner surfaces of these wallsexcept for the reflectors being smooth ground or fine ground. Also, theangular portion lid of wall ii has a sandblasted inner surface 29, thewidth a of this surface being equal to the diameter of apertures i5 andalthough the height of this surface does not necessarily need to belimited to the dimension (1, but may if desired cover the full height oftank it; this reflector I9 may therefore be rectangular rather thancircular.

Tank it i filled with mercury. The reflectors ll, it and it are locatedwith respect to each other to produce a compressional wave beam path asindicated by the lines and arrows in 5. This may be done by taking intoaccount the angle betwen the input transducer and wall r fa t that theangles of incidence are equal to the responding angles of reflection. Asmay be seen in Fig. 5, this design employs sixteen traverses of thetank, with the beam first bouncing back and forth between walls i i andit in a substantially vertical direction in Fig. 5, and then bouncingback and forth between walls i2 and id in a substantially horizontaldirection in said figure, the change in direction being effected by theangular wall portion 5 la. Thus, in this modification there is travel ofthe energy in two separate directions through the mercury, utilizing themercury still more efficiently than the modification of Figs. 2 and 3and resulting in substantially a twofold improvement over the previousembodiment. For the same time delay, the quantity of mercury necessaryis substantially less in the embodiment of Figs. and 5 than in theembodiment of Figs. 2 and 3.

In the embodiment of Figs, 4-5, as in the previous embodiment described,the energy path is uniquely defined (thus substantially preventingspurious paths) by the beam clipping action, because the diameters ofthe reflectors i; and I8 are the same as the diameter of thetransmitting tran ducer and because the reflectors I? and I8 are allsurrounded by highly absorbing and substantially non-reflecting smoothground steel areas.

The beam clipping or beam control technique of this invention is equallyapplicable to solid delay lines. Thus, if a block of fused quartz havingthe configuration shown in Fig. 5 is used, it is possible to solder ametal having an acoustic impedance rather close to that of quartz, suchas lead, for example, onto the sides of the quartz in areas whereabsorption is wanted (that is, where the beam spreads beyond itsoriginal diameter), leaving the quartz-air interface (at which there isa large mismatch in acoustic impedances) in areas where reflection isdesired.

It has been stated above that there is some reflection of energy by thesmooth steel areas, though this is very small indeed as compared to theamount of energy reflected by the sandblasted areas. It has been foundthat energy falling outside of the reflectors on the fine ground steelsuffers a db loss on reflection from such areas. Figs. 6 and 7illustrate a modification whereby such loss may in effect be increased.

Tank 2" is similar to tank l and has a pair of similar opposite sidewalls, only one of which is shown at 8. A plurality of spacedsandblasted circular reflectors 9 is provided on the inner surface ofside wall d, these reflectors being similar to those of Figs. 2 and 3.An annular recess or trough 2i), which may be termed a moat, is cutaround each sandtlasted reflector 9 into the body of wall 8 from theinner face thereof, the bottom of each trough being smooth. As shownmore particularly in Fig. 7, the bottom of each trough is inclined withrespect to its corresponding reflector 9 or with respect to the innersurface of wall 8', since in this, as in all previous modifications, thesandblasted reflectors are coplanar with the inner faces of theircorresponding walls. Each trough 2c is inclined in such a direction thata line perpendicular to the plane of the bottom of the trough pointstoward the bottom end of wall 8' or toward the bottom of tank I.

The unwanted spread or divergent energy impinges on these troughs whichsurround each reflector. Due to the fact that troughs are inclined asabove described, the small portion of this spread energy which isreflected therefrom (which portion is approximately -6 of the totalenergy impinging thereon, since the troughs have smooth steel bottoms)is reflected from the bottom of the trough toward the bottom of the tankl. This energy which is diverted toward the bottom of the tank iseffectively eliminated as far as the signal-responsive path between theinput and output transducers is concerned, since such energy is divertedentirely beyond the effective range of the output transducer. When aconstruction in accordance with that just described, with inclinedtroughs 20, was tested, it was found that the spurious path energieswere more than 50 db down. The unwanted spread energy which is divertedtoward the bottom of the tank is dispersed thereat by multiple travelsthrough and attenuation by the mercury and the walls and, at any iseffectively prevented from interfering with the energy flowing betweenthe two transducers in the tank.

It has been stated previously that this invention is applicable equallywell to liquid and solid delay lines. It is desired to be made clear, atthis juncture, that the moat construction of Figs. 6-? may be utilizedin such solid lines, as well as in liquid lines.

Figs. 8-12 illustrate a modified construction according to thisinvention, in which a plurality, here shown as three, of separate orindependent delay lines are operative in a singe common pool of mercury,and in which, also, the effective lengths of each of the delay lines areindependently adjustable Within a certain range, from outside the tank.

A hollow prismoidal stainless steel tank 2!, of rectangular outerconfiguration, is formed by fastening together four planar sides to formthe 10 body thereof, as by means of bolts 22 and dowel pins 23. Thesides are finished to a tolerance sufficient to provide leak-proofjoints therebetween, and sufficient to make the two ends of theresulting open-ended elongated hollow rec-.

tangular prismoid substantially parallel. The opposite ends of theaforesaid hollow prismoid are closed by means of opposite stainlesssteel end plates 25 and 25, which are fastened to the open ends of thebody in a leak-proof manner. Plates 24 and 25 will be described morefully hereinafter. When the end plates have been secured to the body ofthe tank, a leak-proof tank is provided, and for use this tank is filledwith mercury.

End plate or end wall 24 may be termed the input end of the device,since it has mounted thereon a plurality of input electromechanicaltransducers 26, 2? and 28, while end plate or end wall '25 may be termedthe output end of the device, since it has mounted thereon a pluralityof output electromechanical transducers 2'9, 3t and if. It is to beunderstood, however, that all of the transducers are exactly alike andmay be used interchangeably as receiving or,

transmitting tranducers, or as input and output transducers.

Fig. 10 is a face or front View of one end of the tank. End wall 2:3 maybe fastened to the body of the tank in a leak-proof manner by means ofbolts 32 which pass through spaced apertures provided in said end walland thread into corresponding aligned tapped holes provided in thecorresponding end of the tank body, and also by means of dowel pins 34secured to the tank body and passing through suitabl apertures 33provided in end wall 24.

Fig. 9 is a face or front View of the opposite end of the tank.Similarly, end wall 25 is fastened to the body of the tank in aleak-proof manner by means of bolts 32 which pass through spacedapertures provided in said end wall and thread into correspondingaligned tapped holes provided in the corresponding end of the tank body,and also by means of dowel pins 3d secured to the tank body and passingthrough suitable apertures 33 provided in end wall 25.

A counterbored tapped filler and drain hole 35 is provided in each ofthe end walls 24 and 25, the one in wall 24 being omitted in order tosimplify the drawing. Th se holes are provided in order to fill anddrain the mercury tank. When the tank 2! is filled with mercury, theseholes are closed by bolts which thread into said tapped holes.

The outer faces of the rectangular ens. walls 2 1 and 25 are notparallel to their inner faces, but as shown in Fig. 8 are both somewhatroofshaped with respect to the horizontal center lines which areparallel to their longer sides. In other words, the outer faces of thesewalls beveled inwardly a few degrees from each side of their horizontalcenter lines, thus making their maximum thickness at their center linesand their minimum thickness at their upper and lower ends, theirthickness at their upper ends being equal to their thickness at theirlower ends. The reason for this beveling will appear hereinafter.

Transducer assemblies 25 and Zl are mounted on end wall 24 above thehorizontal center line of said wall and are equally spaced from thevertical center line of said wall on opposite sides of vertical centerline. Transducer assembly 28 is mounted on end wall 2d below thehorizontal center line 0;" said wall with its center on the verticalcenter line of said end wall. Transducer assemblies 25, and are mountedon end wall 25 oppositely with respect to those on end wall 24,transducer assemblies 3i? and SI being mounted below the horizontalcenter line of wall 25 equally spaced from the vertical center line ofsaid wall on opposite sides of said vertical center line, and transducerassembly 29 being mounted above the horizontal center line of wall 25with its center on the vertical center line of said wall.

Transducer assemblies 26-43! are all exactly the same are mounted on thecorresponding end walls 2t and 25 in exactly the same manner; thereforeonly one of such assemblies will be described in detail.

Transducer assembly 2? includes a substantially cup-shaped housing 35which is secured to the outer surface of end wall 2 by means of threecircularly-arranged equally-spaced mounting bolts 3'? which pass throughsuitable holes provided in housing 3% and thread into correspondingtapped holes 38 which are provided in plate 24 and which extend into thematerial of said plate a suitable distance from the outer face thereof.Housing 35 has a central circular opening 35? therein and also a largercentral coaxial circular opening it therein at the inner or righthandend thereof which provides a substantially vertical annular shoulder atthe outer end of aperture ill.

An annular metallic spacer 3! is seated inside aperture 18 and is freeto move therein with respect to housing 35, the outward or leftwardmovement of this spacer being limited by the contactof the outer face ofsaid spacer with the aforesaid annular shoulder and the inward orrightward movement of this spacer being limited by the contact of theinner face of said spacer with the outer face of the metallic end wallor plate 2 3. In order to permit free movement of spacer ll with respectto bolts 3'], three equallyspaced arcuate grooves 32 are cut from theouter edge of spacer :li toward the central opening thereof, thesegrooves being of sufiicient size to allow free movement of spacer l-ipast the corresponding bolts S'i. Spacer i! is adjustable from outsidethe tank to move the same inwardly or outwardly with respect to housing35 and to tilt the vertical faces of said spacer with respect to theaforementioned vertical annular shoulder, to thereby correspondinglymove and tilt the part of the transducer assembly, to be hereinafterdescribed, that bears against spacer ll. This adjustment is madepossible by means of three circularly-arranged equally-spaced adjustingbolts 43 which thread into corresponding tapped apertures in housing 38and the inner ends of which bear against the spacer 4!. Each of thebolts a3 is preferabl spaced half-way between the two adjacent mountingbolt 3?. The tapped aperture for bolts $5 in housing 36- open at theouter face of said housing, so that bolts 53 are manipulable from theoutside of wall 24; the desired movements and tilting of spacer fill maybe had by turning each of the three bolts 13 as may be desired. A locknut it is provided on each of the adjusting bolts it.

A sleeve 35 of insulating material is fixedly secured in a circular boreit in wall 2t which extends inwardly from the outer surface of saidwall. A somewhat smaller circular bore fill is coaxial with bore andextends entirely through wall 24, providing a substantially verticalannular should-er i8 at the inner end of bore 435. The

inner end of sleeve d5 abuts said shoulder, and said sleeve has a lengthsuch that its outer end is located slightly inwardly from the outer faceof wall 25.

An annular disk 45 of insulating material has an outer diameter suchthat it is freely movable within sleeve 15, and disk i5 is mounted forsliding movement within said sleeve. A crystal unit @9, consisting of athin quartz crystal disk 59 which abuts the inner face of a metallicbase member is secured to the inner face of disk 35 by suitable means,such as a stud 53 which threads into member 5! and a portion" of whichengages disk 35; crystal unit ie is also mounted for sliding movement insleeve t5. Base member 5! consists of a disk-like body having a centraloutwardly-extending boss thereon. The disk portion of member 5! bearsagainst the inner face of disk #35 as aforesaid, and the boss portion orsaid member extends through the central circular hole of disk 45. Theouter face of disk engages the inner face of spacer 4i and moves withsaid spacer, thereby to cause members t5, 5% and 5| to slide in sleeve55. In order to provide electrical connection to the outer electrode ofcrystal 56, a conducting clip 52 is maintained in electrical contactwith metal member 5| by means of a stud 53 which passes through a holeprovided in said clip and is threaded into a tapped opening provided inthe boss part of member 55. The inner end of a flexible lead, wire 54 iselectrically connected as by soldering to clip 52, this lead wire beingcoaxial with and soldered in a metal tube 55 which passes out of housing36 through a suitable central aperture 56 provided in the outer or baseportion of said housing, aperture 55 having a larger diameter than tube5%. In orde to hold tube 55 in position with respect to housing 3% andto electrically insulate the same therefrom, a sleeve 57 of insulatingmaterial surrounds and is sealed to tube 55 and in aperture 56 ofhousing 35. Tube 55 extends outside of housing 36 and serves as onelectrical connection to crystal 59. The thin quartz disk as has itsinner face directly exposed to and in acoustic and electrical contactwith the mercury in tank 2i by means of bore 6.? which extends entirelythrough wall 2 3, since the crystal unit 58 is positioned in sleeve 35in bore 6, which bore is coaxial with bore ll. A second electricalconnection to crystal 50 may therefore be made through metallic tank 2iand the mercury therein which is in contact with the tank and with thecrystal.

A narrow resilient Washer 58 is also positioned within sleeve 45 and. isfree to move with respect thereto. The outer face of this washer engagesthe inner face of crystal 59 and the inner face of said washer bearsagainst the shoulder 48. This washer, when the transducer is assembledin end wall E l as shown, is normally under compression, so that ittends to expand to its original shape and it exerts a force which tendsto urge the crystal unit at outwardly or to the left in Fig. 12.

As shown, normally the inner face of spacer at is spaced somewhat fromthe outer face of wall or plate 25. When adjusting bolts 23 aretightened, the inner ends of such bolts, bearing as they do on spacerll, force spacer M, disk 35, and crystal unit t9 inwardly or to theright in Fig. 12 against the yielding force of resilient washer 58, disk35' and unit 59 sliding in sleeve 45. As bolts it are tightened more andmore, eventually the inner face of metallic spacer ll comes into contactwith the outer face of metallic wall 23, thus positively stopping anyfurther inward movement of spacer ll by the metal-tometal contact ofmembers ll and 24. In this manner, possible damage to the crystal 50 isprevented, which damage could be produced if sufficient inward pressurewere applied to said crystal to cause it to come into contact withshoulder 48 or to cause it to be forced with too large a pressureagainst washer 58.

Since washer 59 at all times tends to urge the crystal unit it outwardlyor to the left, when adjusting bolts it are loosened Washer 58 ispermitted to expand, pushing crystal unit 59, disk 45', and spacer lloutwardly or to the left in Fig. 12. Thus, by manipulation of bolts 43,crystal unit 59 may be moved outwardly or inwardly; by means of thethree-point pressure on spacer il, the crystal unit iQ may also betilted with respect to housing 35 or end wall 24.

Because of the beveled outer surface of end plate 2%, the inner face ofhousing 36, which bears thereagainst, is tilted at a small angle to theinner face of end wall 2 This means that the inner surface of spacer ll,the inner surface of disk 65, and the quartz disk 59 are similarlytilted at a small angle to the inner surface of wall 2%. As a result,the line E, which is normal to the active face of crystal 50 and whichindicates the direction of travel of the compressicnal wave beamemanating from transducer 21, is directed downwardly at a small anglewith respect to the horizontal or with respect to the upper and lowersides of tank 25.

Transducer assemblies 26 and 28-35 are all exactly similar to transducerassembly 21 described above. The transducers 26 and 29 are both directeddownwardly at a small angle with respect to the horizontal, while thetransducers 28, 3e and Bi are all directed upwardly at a small anglewith respect to the horizontal, due to the mounting of these transducerson the end walls as previously described and to the beveled outersurfaces of the end walls. For example, the receiving transducer 3%responds to energy received from the direction indicated by F in Fig.11.

Three sandblasted circular areas or reflectors 59, 60 and 6!, similar tothe reflectors 9 of Fig. 2, are provided on the inner surface of endplate "2 3. Each of these reflectors may if desired have P the samediameter as the bores M, in accordance with the principles underlying,and for carrying out, the beam clipping technique described inconnection with Fig. 2. However, we have found that, in thethree-traverse design of Figs. 8-12, in which, moreover, the totallength of the compressional wave path is somewhat limited, it is notabsolutely necessary to limit the diameter of the reflectors to theoriginal diameter of the beam, since for lengths of beam travel on thisorder the beam does not diverge sufficiently to establish spurious pathswhich appreciably interfere with the desired operation of the device.For this reason, the diameter of each of the refiector areas 59, til andBI is illustrated as being somewhat greater than the diameter of bores41.

The center of reflector 59 is located somewhat below the horizontalcenter line of end plate 24 and in the same vertical plane as the centerof transducer 25, the center of reflector 60 is located somewhat abovethe horizontal center line of end plate 2 and in the same vertical planeas the center of transducer 23, and the center of reflector 6! islocated somewhat below the horizontal center line of end plate 24 and inthe same vertical plane as the center of transducer 21. How the spacingsof reflectors 59, $9 and 61 with respect to the horizontal center lineof end plate 24 are determined will be explained subsequently. Exceptfor the bores 41 and and for the sandblasted areas 59-6l, the entireinner face of end plate 2d is uninterrupted and is fine ground or groundvery smooth, to provide a highly polished steel surface.

Three adjustable reflectors 62, 63 and 84, which are cylindricalstainless steel plugs having their inner ends sandblasted to providereflecting surfaces, are mounted in output end plate 25. The circularinner face of each of the plugs 62-64 is parallel to the inner face ofplate 25. The di ameter or each of these plugs is equal to the diameterof reflectors 59-81. The center of plug 92 is located somewhat above thehorizontal center line of end plate 25 and in the same vertical plane asthe center of transducer 30, the center of plug 63 is located somewhatbelow the horizontal center line of said end plate and in the samevertical plane as the center of transducer 28, and the center of plug 64is located somewhat above the horizontal center line of said end plateand in the same vertical plane as the center of transducer 3!.

The plugs 62-54 are all alike so only one of them will be described indetail. Plug 62 is mounted for longitudinal sliding movement in acorresponding circular bore 65 which extends outwardly from the innerface of plate 25 and has a depth which is a substantial portion of thethickness of said plate. A cap screw 66 extends through a suitableaperture 61 in plate 25, aperture 61 being smaller in diameter than bore55, being coaxial therewith, and being in communication therewith. Theinner end of screw 66 is threaded into a centrally-located tappedaperture 68 which extends for a suitable distance into plug 62 from theouter end thereof. The inner face of the cap of screw 66 is adapted tobear on a counterbored shoulder provided at the outer end of aperture61. In this way, when screw 66 is tightened, the cap of said screw bearsagainst end plate 25 and plug 62 is moved outwardly or to the right inFig. ll. A resilient washer 69 is positioned between the outer end ofplug 52 and the vertical shoulder provided at the outer end of bore 65,this washer being normally under compression so that it tends to expandto its original shape and to thereby exert a force which tends to urgethe plug $2 inwardly or to the left in Fig. 11. When screw 66 istightened, plug 62 is moved to the right or outwardly against theyielding force of Washer 69, plug 62 sliding in bore 55. When screw 66is loosened, washer 59 is permitted to expand, pushing plug 62 inwardlyor to the left in Fig. 11. The compressional wave beam emanating fromthe input end 2% of the tank is adapted to impinge on the reflectingsurface of plug 62 and be reflected thereby, as indicated by lines G andH, respectively. It may be seen that, by moving plug 62 in and out withrespect to end plate 25 or toward and away from end plate 24, the lengthof the path traversed by the compressional wave energy in the tank 2! iscorrespondingly decreased or increased, thereby decreasing or increasingthe time delay of the portion of the tank involving plug 62.

Means are provided both for limiting the range of movement of plug 62and also for preventing rotation of said plug when screw 66 is rotated.A substantially rectangular slot 10 is cut into the cylindrical wall ofplug 62, this slot having a desired depth and a length equal to thedesired range of movement of said plug; this slot is closed at both endsby the material of the plug. A vertical hole is drilled downwardly fromthe upper end face of end plate 25 into communication with bore 65, anda portion of the length of this hole is threaded. A stud H is threadedinto this hole, said stud having a shank portion Ha which extends downinto bore 65 and which is of such diameter as to fit nicely into boreill of plug 62. The inward and outward movements of plug 52 are limitedby engagement of shank portion Ha with the outer and inner end wallsurfaces of slot 78. At the same time, as adjusting screw 66 is turned,the plug 62 is effectively prevented from rotating also by theengagement of shank portion lid with the side edges of slot 70.

Plugs 53 and 6 3 are both adjustable, have exactly the same constructionas plug 62, and are mounted in end plate 25 in exactly the same way asplug 62, except that the hole for the stud 'II which coacts with plug 63is drilled upwardly from the lower end face of plate 25, since plug 63is below transducer 29, while plugs 52 and 64 are above the respectivetransducers 3i] and Bi.

Except for apertures s? and 35 and plugs 6254, the inner face of plate25 is uninterrupted and is ground smooth.

The tank 2! has three separate delay lines utilizing the same body orpool of mercury, and each line employs three traverses lengthwise of thetank. Input transducer 27 cooperates with output transducer 36 toprovide one delay line, input transducer 28 cooperates with outputtransducer 29 to provide a second delay line, while input transducer 25cooperates with output transducer 3i to provide a third delay line. Thecircular reflectors 5964 are so located on their corresponding endplates 24 and 25 that, taking into account the angle of bevel of theouter surfaces of such plates and the consequent tilt of transducersZfi-Bi, the length of the tank 2i, and the fact that the angl ofincidence of the compressional wave beam on a reflecting surface isequal to the angle of reflection from such surface, reflectors 826-iwill each receive a beam from a corresponding transmitting transducer26-28 and will reflect the beam to a corresponding reflector 59- whilereflectors 596I will each receive a beam from a corresponding reflector62-64 and will reflect the beam to a corresponding receiving transducer29-3l.

Now referring to Figs. 11-12, the beam of compressional wave energy forone of the delay lines emanates from the crystal 5% of transmittingtransducer 2? along the line E, which is inclined downwardly at a smallangle to the horizontal, travels to the opposite end 25 of the tank,impinges on reflector plug 62 along line G, is reflected therefrom alongline H, travels to end 24 of the tank, impinges on integral reflector 6!along line J, is reflected therefrom along line K, travels to end 25 ofthe tank, and impinges on the crystal 5B of output or receivingtransducer 33 along line F. It will thus be noted that this beam fromtransducer 2'! travels back and forth three times across the tank anddownwardly from transducer 2? to transducer 38. The path betweentransducers 2? and 35 is indicated by dotted lines in Fig. 8.

Similarly, the third delay line path includes 16 input transducer 26,plug reflector E4, integral reflector 59, and output transducer 3!, thisbeam also traveling back and forth three times across the tank anddownwardly from transducer 26 to transducer 38.

The second delay line path includes input transducer 28 (which isinclined upwardly at a small angle with respect to the horizontal), plugreflector 63, integral reflector 6i), and output transducer 29, thisbeam traveling back and forth three times across the tank and upwardlyfrom transducer 28 to transducer 29. The path between transducers 28 and29 is indicated by dot-dash lines in Fig. 8.

From the above, it may be seen that, in the structure of Figs. 842,three separate or independent delay lines are provided in a single tankof rectangular prismoidal shape, this tank containing a single pool orbody of mercury which is common to all three lines. All of the mercuryin the tank is maintained at the same temperature by normal convectioncurrents. Therefore, the velocity of travel of the compressional wavesin the mercury is exactly the same for all thre lines, thus compensatingfor differences in the lines due to thermal eifects; such differences invelocity could easily arise due to slight differences in temperatures ofthe separate mercury pools if separate pools or tanks were used for,each of the three lines.

By manipulation of any of the separate screws E6, the corresponding plugreflectors 62-54 may be moved inwardly or outwardly as desired, tothereby vary the length of the corresponding delay line or the amount ofdelay of the corresponding line. In this way, differences between thethree lines due to natural manufacturing tolerances or to circuitdissimilarities may be compensated for. Also, since the crystal units ofeach of the transducers 26-4! are adjustabl inwardly and outwardly andalso for tilt, the input transducers of each delay line may be properlyaligned with their corresponding output transducers.

If tank it is entirely filled with mercury and sealed, an air-filledexpansion tank (not shown) is preferably provided thereon, to allow forcontraction and expansion of the mercury induced by temperaturevariations.

Fig. 13 is a block diagram of a portion of a moving-target-indicator(MTI) radar system utilizing a mercury delay lin according to thisinvention. Incoming video intelligence, such as the output of a radarreceiver, is applied to a modulator '52, to which is also applied acarrier wave from an oscillator 73 in order to produce a modulatedcarrier signal in line it. As previously stated, it is not absolutelynecessary to use the oscillator '53 or the modulator 12; if thesecircuit components are omitted, the incoming video intelligence may bapplied directly to point 35. At point E5, the modulated carrier issplit applied to two separate channels, one consisting of a mercurydelay line it, an ampliiier H, a detector l3, and an output resistor 79,and the other consisting of an attenuator 80, an amplifier 8!, adetector 82, and an output resistor 3 which is connected in seriesopposition to resistor la.

Delay line is is constructed according to this invention and functionsto delay the intelligence for a time corresponding to the periodicity ofthe radar transmitter, producing at its output delayed videointelligence which is amplified, de tected, and applied to resistor '19,Attenuator .80

has an attenuation equal to that inherent in delay line 16 but providesno delay, so that undelayed video intelligence is provided at the outputthereof, this intelligence being amplified, detected, and applied toresistor 83. When there are no moving targets within the field of searchof the radar equipment, successive echo signal patterns are exactlyalike and th undelayed and the delayed video intelligence are exactlythe same so that they cancel each other, producing zero signal output atpoint 84 between resistors 19 and 83. On the other hand, when there aremoving targets within the field of search, successive echo signalpatterns are not alike and the undelayed and the delayed videointelligence are dissimilar so that they no longer cancel each other,producing an output signal at point 84, which signal is applied to asuitable indicator (not shown).

Fig. 14 illustrates the z-ipplication of the delay line construction ofFigs. 8-12 to the storage or memory portion of a computing system. InFig. 14, parts the sam as those of Figs. 812 are referred to by the samereference numerals. The tank 2! of Fig. 14 is in effect reversed with respect to that described previously, in that in the Fig. i l circuittransducers 3B, 29 and M are transmitting or input transducers whiletransducers 2'5, 28 and 23 are receiving or output transducers. However,as previously stated, transducers 2-3l are all exactly alik and may beused for either transmitting or receiving ultrasonic compressional waveenergy. The first delay line path through tank 25 is from inputtransducer 30, to fixed reflector 61, to adjustable reflector 62, tooutput transducer 21. The second delay line path is from inputtransducer 29, to fixed reflector ed, to adjustable reflector 63, tooutput transducer 28. The third delay line path is from input transducer31, to fixed reflector 59, to adjustable reflector 64, to outputtransducer 26.

The first delay line channel between transducers 39 and 21 is used as acontrol channel, and for this purpose a reference signal is sup, pliedto input transducer 39 through a modulator and driver circuit 85, and isalso supplied to one input connection 86 of a phase detecting circuit81. The delayed reference signal picked up by output transducer 2'! isapplied through an amplifier 88 to the second input connection 89 ofcircuit 81. Circuit 81 produces at its output connection 90 a signaldependent on the phase relas tion between the two inputs 88 and 89, andthis relation depends in turn on the time delay between transducers 39and 21 in the mercury tank 21, The output connection may be applied to atemperature control for the mercury in tank 2!, or it may be applied toa frequency control for the drivers 85, 9| and [03.

The second delay line channel between transducers 29 and 28 may be usedfor storing a series of electrical impulses representing digits, thetime duration of the entire series beingequal to the time delay providedin the tank between said transducers and the series of impulses beingrepetitively transmitted and retransmitted through said channel. Forthis purpose, the signal output of a modulator and driver circuit 9| isapplied to input transducer 29. Th delayed signal picked up by outputtransducer 28 is applied through an amplifier 92 to a reshaping gate 93,to which clock pulses from a suitable source are also applied. Theoutput of the-reshaping ate 93 is a pli d t o gh an e as gate 99,

18 which is actuated by .means of suitable control signals, to the inputconnection of driver circuit 9i, so that the series of impulses istransmitted again and again through the second delay line channel bymeans of the loop just described. When the erase gate at is properlyactuated by the control signals applied thereto, this loop is in effectbroken and a certain impulse or certain impulses are efiectively erasedircm channel.

The signals stored in this channel may be utilized by means of a readgate connected to the output of reshaping gate '93 and actuated bysuitable control signals applied thereto at 9B; th signals appear in theoutput connection 91 of read gate 95, which connection is connected topoint 98.

In order to write signals into this memory or storage system, a writegate 99 has its output connected to point I00 between gate 94 and driver9!. Gate 99 is supplied from a memory write-in lead H3! and is actuatedby suitable control signals supplied through connection 32.

An arrangement similar to that described for the second delay linechannel is provided for the third delay line channel between transducers3| and iii. The output of modulator and driver circuit I03 is applied toinput transducer 3|, the delayed signal picked up by output transducer226 being applied through an amplifier Hi4 to a reshaping gate tilt:supplied with suitable clock pulses. The output of gate W5 is appliedthrough erase gate "is to the input connection of driver circuit I63,gate me being actuated by suitable control signals. Read gate I0? isconnected to the output of gate H35 and is actuated by control signalsapplied thereto at 38. The output connection Hit of gate It? isconnected to point 98. Write gate H0 has its output connected to pointHI between gate I06 and driver H13. Gate H0 is supplied from memorywrite-in lead it]! and is actuated by control signals supplied throughconnection H2.

In the system of Fig. 14, two memory or signal storage channels areprovided, along with one control channel, these three delay linechannels utilizing a single common pool or body of mercury in accordancewith the construction illustrated in Figs. 8-12.

Of course, it is to be understood that this invention is not limited tothe particular details as described above, as many equivalents willsuggest themselves to those skilled in the art. For example, althoughthis invention has been described in connection with compressional wavesin the longitudinal mode in liquids, it is equally applicable to soliddelay lines, and, when such solid lines are used, transverse or shearmode waves may be utilized if desired, according to the principlesset'forth herein. Various other variations will suggest themselves. Itis accordingly desired that the appended claims be given a broadinterpretation commensurate with the scope of this invention within theart.

What is claimed is:

1. A delay line, comprising a metallic tank having at least one smoothinternal" wall, a compressional wave transmitting medium in said tank,an input transducer acoustically coupled to said medium, through a wallof said tank, the portion of said transducer which is coupled to saidmedium having a limited area andbeing arranged to project .a beam ofcompressional wave energy having a cross, section commenu ate with aidreatoward said smooth wall, a roug m a series? of l mite area, om.-

parable to the area of said portion, mounted on said smooth wall toserve as a reflecting surface for compressional waves, said roughsurface being so located that a compressional wave beam emanating fromsaid input transducer and traveling in said medium impinges on saidsurface and is reflected toward a region closely adjacent said inputtransducer, and an output transducer acoustically coupled to saidmedium, said smooth wall providing a reasonably good acoustic match tosaid medium and said rough surface providing substantially a mismatch tosaid medium.

2. A delay line, comprising a tank having first and second opposingparallel walls, a compressional wave transmitting medium in said tank,an input transducer acoustically coupled to said medium through saidfirst wall and adapted to provide a beam of compressional wave energydirected toward said second wall, the portion of said transducer whichis coupled to said medium having a limited area, a first reflectingsurface of limited area, comparable to the area of said portion, mountedon said second wall of said tank and so located that a compressionalWave beam emanating from said transducer and traveling in said mediumimpinges on said surface, the material of said wall surrounding saidsurface having an acoustic impedance which provides a reasonably goodacoustic match to said medium, a second reflecting surface of limitedarea, comparable to the area of said portion, mounted on said first wallof said tank closely adjacent said input transducer and so located thatthe beam reflected from said second surface impinges on said second wallin a region closely adjacent said first surface, the material of saidfirst Wall surrounding said second surface having an acoustic impedancewhich provides a reasonably good acoustic match to said medium, and anoutput transducer acoustically coupled to said medium at said region insaid second wall, said tank being devoid of interior partitions withinthe body of said medium.

3. In combination, a single body of homogeneous uninterruptedcompressional wave transmitting medium totally devoid of any internalpartitioning members, a plurality of directional input transducersacoustically coupled to said medium, each of said input transducersadapted when energized to project a beam of compressional wave energy oflimited cross-sectional extent into said medium, an equal number ofdirectional output transducers acoustically coupled to said medium, eachone of said input transducers being directed to transmit compressionalwave energy to a corresponding one of said output transducers, and areflector located to reflect the beam from each input transducer to itscorresponding output transducer, said reflector being of substantiallythe same shape and area as the cross section of said beam, whereby aplurality of separate and independent delay lines are provided whichutilize in common said single medium.

4. In combination, a tank devoid of interior partition members andcontaining a single body of homogeneous uninterrupted compressional wavetransmitting fluid, a plurality of directional input transducers mountedin said tank and acoustically coupled to said body, each of saidtransducers adapted when energized to project a beam of compressionalwave energy of limited cross-sectional extent into said body, an equalnumber of directional output transducers mounted in said tank andacoustically coupled to said body, each one of said input transducersbeing directed to transmit compressional wave energy to a correspondingone of said output transducers, and a reflector located to reflect thebeam from each input transducer to its corresponding output transducer,said reflector being of substantially the same shape and area as thecross section of said beam, whereby a plurality of separate andindependent delay lines are provided which utilize in common said singlebody.

5. In combination, a tank containing a body of compressional wavetransmitting fluid, a plurality of directional input transducers mountedin said tank and acoustically coupled to said body, an equal number ofdirectional output transducers mounted in said tank and acousticallycoupled to said body, each one of said input transducers being directedto transmit compressional wave energy to a corresponding one of saidoutput transducers, whereby a plurality of separate delay lines areprovided, a separate movable reflector for each of said lines mounted insaid tank, each reflector being so located that a compressional wavebeam traveling in said body between its corresponding input and outputtransducers impinges on such reflector, and separate means forindependently moving each of said reflectors at will toward or away fromone of its corresponding transducers.

6. In combination, a tank having a pair of opposite walls, a body ofcompressional wave transmitting fluid in said tank, a plurality ofdirectional input transducers acoustically coupled to said body, anequal number of first refleeting surfaces associated with one of saidwalls, each of said surfaces being so located that a compressional wavebeam emanating from its corresponding input transducer and traveling insaid body impinges on such surface, an equal number of second reflectingsurfaces associated with the other of said walls, each of said secondsurfaces being so located that the beam reflected from its correspondingfirst surface impinges on such second surface, an equal number ofdirectional output transducers acoustically coupled to said medium toreceive the energy which has been reflected by its corresponding secondsurface, whereby a plurality of separate delay lines are provided, thereflecting surfaces constituting one group each being separately movablewith respect to the corresponding wall, and separate means forindependently moving each of said movable reflectors at will toward oraway from one of its corresponding transducers.

7. A delay line comprising a compressional wave transmitting mediumhaving boundaries, means at a first boundary for introducing asubstantially directive beam of compressional waves into said mediumpropagating in a first direction toward a second boundary, said beamhaving initially a prescribed cross-section, said boundaries being of acharacter such that said waves arriving at either boundary through saidmedium are substantially not reflected thereby, a first compressionalwave reflective means at said second boundary in the path of said beamdisposed to reflect said beam in a second direction toward a location atsaid first boundary other than the location of the wave introducingmeans, and a second compressional wave reflective means at said firstboundary in the path of said beam disposed to reflect said beam in athird direction toward a location at said second boundary other than thelocation of said firstacefaoerr reflective means,saidmeflectivemeanseach haw ing a reflective zarea substantially 1commensurate with said prescribed cross-section of said beam.

8. A delay'line according to olaim' l' in which said :medium 31Scontinuous and completely devoid of partition members of .any kindwithin said boundaries.

9. -A delay line comprising a compressional wave transmitting mediumhaving boundaries, means at a flrst boundar-yfor introducing asubstantially-directive beam of :compressional waves into said mediumpropagating :toward a second boundary in a first =direotion making anearlynormal angle with said .second :boundary, said beam :havinginitially a prescribed cross-section, a :first compressional wavereflective means at said second boundary in the pathlofsaid beamdisposed to reflect said beam in a second direction toward a -=locationat said first boundary closely adjacent .to the location of the waveintroducing means, a second compressional wave reflective means at saidfirst boundary in .the path of said 'beam disposed to reflect said beamn a third direction parallel to said first .direction toward .a locationat said second boundary closely adjacent the -location of said firstreflective means, said reflective means each having .a reflecting areasubstantially commensurate with said prescribed cross-section of saidbeam, and means surrounding each reflecting area for removing waveenergy of the incident beam falling outside the reflecting area.

10. A delay line comprising a homogeneous continuous body of acompressional Wave transmitting medium, means at a-first location insaid medium for introducing a substantially directive beam ofcompressional waves into said medium propagating in a first directiontoward a second location, said beam having initially a prescribedcross-section, a first compressional wave reflective means located atsaid second location disposed to reflect said beam in a second directiontoward a third location closely adjacent said first location, a secondcompressional wave reflective means located at said third locationdisposed to reflect said beam in a third direction parallel to saidfirst direction toward a fourth location closely adjacent said secondlocation, said reflective means each having a reflecting areasubstantially commensurate with said prescribed cross-section of saidbeam, and means surrounding each reflecting area for removing waveenergy of the incident beam falling outside the reflecting area.

11. A delay line comprising a homogeneous continuous body of acompressional wave transmitting medium, means at a first location insaid medium for introducing a substantially directive beam ofcompressional waves into said medium propagating in a first directiontoward a second location, said beam having initially a prescribedcross-section, a first compressional wave reflective means at saidsecond location disposed to reflect said beam with a single reflectionin a second direction toward a third location closely adjacent saidfirst location, said second direction thereby making an acute angle withsaid first direction at said first reflective means, a secondcompressional wave reflective means at said third location disposed toreflect said beam with a single reflection in a third direction parallelto said first direction toward a fourth location closely adjacent saidsecond location, said third direction thereby making an acute angle withsaid second direction at said second reflective means, said reflectivemeans each :having a reflective area substantially commensurate withsaid prescribed cross-section of said ibeam, and means surrounding eachreflecting area for removing wave energy of the incident beam 'fallengoutside the reflecting area, said beam in traversing said medium ;insaid second direction employingin parta portion of the medium traversedby :said beam in said first direction and in :part a portion of themedium to :be'traversed by said beam in said third direction, wherebyplural use of said medium is made :to propagate said beam therethrough.

12. A delay line, comprising a body of :compressional wave-transmittingmaterial having four .rectangularly disposed parallel boundaries, thefirst. and second of ,whichtcons'titute one :pair of iparalleloppositeiboundaries and the .thirdzand fourth'of which constitutear-second pair of parallel .opposite boundaries, and :a fifth boundaryconnecting two adjacent :rectangularly-disposed boundaries and making anangle of fOIftYrfi-VG degrees approximately with .each, an inputelectro-acoustic transducer coupled to said ,medium through a boundaryof said'one pair. and adapted to rprojecta beam of compressional wavestoward its opposite boundary, :means in said opposite boundaries toreflect said beam back and forth therebetween, said ,means beingconstituted by reflectors of area limited .in extent to approximately\the same .size and shape as the cross section of said beam, :a similarreflector :in said fifth boundary disposed to change the direction of:said beam by approximately ninety ,degrees so that said beam. isthereafter reflected back and forth between the boundaries of ,a secondpair of opposite walls, similar reflectors disposed in .said second pairof opposite walls :in positions to :efiect reflection .back andforth .ofsaid beam therebetween and an output electro-acoustic transducer in oneof the walls of said second pair of opposite walls positioned to receivesaid beam after a series of reflections between said one pair and saidsecond pair of opposite walls.

13. A delay line, comprising a metallic tank having a pair of first andsecond opposite substantially parallel walls, a compressional wavetransmissive medium filling said tank and being devoid of interiorpartition members, an electroacoustic transducer mounted in said firstwall and adapted to project a beam of compressional waves into saidmedium toward said second wall, said beam having a cross section offixed area and shape, a reflector in said second wall of substantiallysimilar area and shape disposed in the path of said beam to reflect saidbeam toward said first wall closely adjacent said input transducer, thematerial of said second wall surrounding said reflector being undercutto provide a reflecting surface in a plane difierent from the surface ofsaid reflector, whereby compressional wave energy falling outside saidreflector is reflected in a direction different from the energy fallingupon said reflector, similar reflector means in said first wall adjacentsaid input transducer and an output electroacoustic transducer disposedin one of said walls to receive said beam after repeated reflectionbetween said walls.

14. A delay line comprising a plurality of spaced surfaces bounding acompressional wave transmitting body, one of said surfaces having anoutput transducer associated therewith, and predetermined areasintegrated with other of said surfaces having a substantially greatercoefficient of reflection than the portions of said 23" surfacessurrounding said areas for causing a substantially directive beam ofcompressional waves to traverse said body a predetermined pluralitynumber of times along substantially parallel paths and then emergetherefrom by way of said output transducer.

15. A delay line comprising a plurality of spaced surfaces bounding acompressional wave transmitting medium, a first surface portion of saidsurfaces having a signal input transducer coupled thereto forintroducing a substantially directive beam of compressional wave energypropagating toward and reflecting successively from a plurality of areasof said spaced surfaces, said areas having a substantially greatercoefficient of reflection than the portions of said surfaces surroundingsaid areas, and a signal output transducer coupled to a second surfaceportion of said surfaces and intercepting said beam successivelyreflected from said plurality of areas.

16. A delay line comprising a plurality of spaced surfaces bounding acompressional wave transmitting homogeneous body substantially devoid ofintruding wave reflecting discontinuities throughout the entire internalvolume thereof, one of said surfaces having an output transducerassociated therewith, and predetermined areas integrated with other ofsaid surfaces having a substantially greater coefficient of reflectionthan the portions of said surfaces surrounding said areas for causing asubstantially directive beam of compressional waves to traverse saidbody a predetermined plurality number of times along substantiallyparallel paths and then emerge therefrom by way of said outputtransducers.

17. A delay line comprising a plurality of spaced surfaces bounding acompressional wave transmitting medium, a first surface portion of saidsurfaces having a signal input transducer coupled thereto forintroducing a substantially directive beam of compressional wave energypropagating toward and reflecting successively from a plurality of areasof said spaced surfaces, said areas having a substantially greatercoerficient of reflection than the portions of said surfaces surroundingsaid areas and said portions of said surfaces surrounding said areashaving compressional wave energy absorbing means coupled thereto forabsorbing energy at a substantially greater rate than said medium, and asignal output transducer coupled to a second surface portion of saidsurfaces and intercepting said beam successively reflected from saidplurality of areas.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,616,639 Sprague Feb. 8, 1927 2,155,659 Jeflree Apr. 25, 19392,263,902 Percival Nov. 25, 1941 2,421,026 Hall et a1. May 27, 19472,423,306 Forbes et al. July 1, 1947 2,447,485 Biquard Aug. 24, 19482,505,364 McSkimin Apr. 25, 1950 OTHER REFERENCES UltrasonicMeasurements of the Compressibility of Solutions and of Solid Particlesin Suspension, by Chester R. Randall, Bureau of Standards Journal ofResearch, vol. 8, pages 79-96, January 1932. (Copy in Patent OfficeLibrary.)

